1. Field of the Invention
The invention is directed to compatible blends of polyamides and aromatic carbonate polymers useful as thermoplastics, and methods for making each compatible blends.
2. Brief Description of the Prior Art
Much effort has been expended on the problem of blending polyamides (especially nylons) with aromatic carbonate polymers (especially polycarbonates). Such blends and alloys are particularly useful for achieving simultaneously the good impact strength and dimensional stability characteristic of the carbonate polymers and the good solvent resistance, toughness, ease of processing and resistance to environmental stress cracking characteristic of the polyamides.
These two classes of polymers are normally not miscible, at least not without unacceptible delamination. In order to achieve miscibility and to obtain useful blends which exhibit no tendency to delaminate, various strategems have been used. One method is to utilize a relatively more compatible type of amorphous polyamide as taught by Maresca et al. U.S. Pat. No. 4,798,874 (Jan. 1989). Another method is to compatibilize a polyamide with a polycarbonate or polyester carbonate by use of an effective amount of a polyamide-polyester block copolymer as taught by Maresca et al. in U.S. Pat. Nos. 4,788,248-9 (Nov. 29, 1988), or by use of an effective amount of a polyetherimide, a polyurethane or certain linear segmented thermoplastic elastomers as taught by Perren et al. in U.S. Pat. No. 4,782,114 (Nov. 1, 1988).
It has also been shown by Maresca, Eur. Pat. 227053 (July 1 , 1987) that a compatibilizing agent with epoxy functional groups is useful for compatibilizing a polyamide with a carbonate polymer. However, this effect is not as complete as desired because the usual carbonate polymer lacks functional groups for chemical interaction with the epoxy compatibilizing agent.
In order to make this type of polyamide/polycarbonate block copolymer required as a compatibilizing agent, it it necessary to find a means of creating a functionalized polycarbonate onto which the polyamide segment can be attached by means of the functional chain ends of the polyamide, which are normally carboxyl and amino groups. Normally, aromatic carbonate polymers lack functional end groups. It is however known that aromatic carbonate polymers can be made having carboxyl end groups or ester side groups. The present invention offers an effective and convenient means for attaching the carboxyl or ester end groups of such an aromatic carbonate polymer to the end groups of the polyamide (polyamide), thus providing a graft polyamide-polycarbonate for use as such as a thermoplastic or for use as a compatibilizing agent in blending of polyamides with aromatic carbonate polymers.